dissapearing geometry with scrolling
It looks like you need to adjust your camera clipping distance.

Select your camera and change the clipping end until you can see the full geometry.



If that doesn't work it's likely that you changed your viewport clipping.
In the viewport press 'N' to open up the side bar. Under 'View' edit the clipping distance as shown above.

You can change the clipping based on centimeters by changing the unit preset to centimeter. This can be done under the 'Scene tab':